wrote in message
.. .
I recently replace the impeller in the sea water pump of the
4-108 on a
boat I bought recently. Should there be a gasket to replace as
well?
This pump has the speed seal quick remove cover. Looking through
catalogs and shelves of boat stores I don't see gaskets for it.
The
impeller came in a small box of its own with no gasket for the
housing.

If that leaves you with a metal cover pushing against a metal
body, it'll leak, and without a gasket, may jam the impeller.

When you took the cover off, was there a thin paper gasket in
place? Perhaps which came apart and just looked like gunge (which,
of course, being a tidy fellow, you scraped off) after you prised
the lid off?

It is also just possible that the Speed Seal design has been made
to work with a rubber ring gasket (I don't know them), but in that
case there would be a groove in the cover to locate the ring, and
the centre of the cover would be slightly proud compared to the
mating surface.

So a quick check of the cover will tell you what type of gasket to
get. With care, and knowing the appropriate thickness (I think
yours would be 0.3mm, but check with Jabsco), you can make your
own. Oil some paper, punch holes in place to mate with the bolts,
very gently tap the paper against the pump face edges with a small
hammer (preferably lead!), remove the paper and cut any edges that
the hammer didn't cut. and there's your gasket.

Or go and buy a whole lot in one go . . .
--
JimB
http://www.jimbaerselman.f2s.com/
for opinions comparing Greek cruising areas